There are many types of Rankine cycle loops and more particularly those involving a (liquid/vapour) phase change of a working fluid.
This type of cycle generally consists of a stage wherein the working fluid used in liquid form is compressed in an isentropic manner, followed by a stage where this compressed liquid fluid is heated and vaporized on contact with a source of heat.
This vapour is then expanded, in another stage, in an isentropic manner in an expansion machine, then, in a last stage, this expanded vapour is cooled and condensed on contact with a cold source.
To carry out these various stages, the loop comprises a compressor pump for circulating and compressing the fluid in liquid form, an evaporator that is swept by a hot fluid for at least partial vaporization of the compressed fluid, an expansion machine for expanding the vapour, such as a turbine that converts the energy of this vapour to another energy such as a mechanical or electric energy, and a condenser by means of which the heat contained in the vapour is yielded to a cold source, generally outside air that sweeps this condenser so as to convert this vapour to a fluid in liquid form.
In this type of loop, the fluid used is generally water but other types of fluid can also be used, for example organic fluids or organic fluid mixtures.
By way of example, these organic fluids can be butane, ethanol, hydrofluorocarbons, ammonia, carbon dioxide, etc.
It is also well known, notably through document FR-2,884,555, to use the calorific energy conveyed by the exhaust gas of internal-combustion engines, in particular those used for motor vehicles, as the hot source providing heating and vaporization of the fluid flowing through the evaporator.
This allows to improve the energy efficiency of this engine by recovering a large part of the energy lost at the exhaust in order to convert it to an energy that can be used for the motor vehicle through the Rankine cycle loop.
In some instances, the working fluid is caused to circulate at high pressures (up to about 40 bars or even 80 bars) and very high temperatures, close to 400° C. These fluid pressures and temperatures are maintained within the operating range for which the system is dimensioned by means of a control system that acts notably upon the pump, the expansion machine and on the actuators driving the various elements of the loop.
Furthermore, when using certain working fluids, this fluid may also appear to be intrinsically dangerous, notably flammable.
Thus, in case of an abnormal situation of the vehicle, an accident for example, the system controlling the Rankine cycle loop can become inoperative, either as a result of a malfunction of the control system itself or of a malfunction of the sensors or the driving actuators.
Due to the thermal inertia of the hot source or after a vehicle fire that may occur during an accident, the pressure and the temperature of the working fluid can continue to increase. In this case, temperature or pressure levels of this fluid incompatible with the dimensioning of the Rankine system can be reached. These levels can lead to a sudden break in one or more elements of the loop (fluid circulation line, exchanger, etc.), thus causing yet another accident.
The present invention aims to overcome the aforementioned drawbacks by means of a method allowing to take preventive measures so as to limit or even to prevent a closed loop break.